1. Field of the Invention
The present invention relates to micro-electromechanical systems (MEMS) and, more specifically, to reinforcing struts for MEMS structures.
2. Description of the Related Art
MEMS mirror arrays find applications in optical switches, adaptive optics, displays, etc. One advantageous characteristic of a MEMS mirror array is that each mirror can have many degrees of freedom in a relatively small footprint and be of high optical quality. The high optical quality is achieved, e.g., by making each mirror relatively smooth, flat, and highly reflective. Surface smoothness is usually achieved by chemical-mechanical polishing. High reflectivity is achieved using optically reflecting coatings, e.g., made of aluminum or gold. However, the overall mirror flatness is relatively difficult to achieve due to stress-gradients in the mirror material itself and stress mismatches between the mirror material and the material of the optically reflecting coating.
One known way to reduce stress-induced mirror deformations is to have one or more reinforcing beams (struts) attached to the backside of the mirror. A typical prior-art reinforcing strut has a uniform rectangular cross-section and runs from one edge of the mirror to the opposite edge. However, one problem with such struts is that they can significantly (i) increase the moment of inertia of the mirror, thereby disadvantageously increasing the mirror's response time to control signals, and (ii) limit the range of motion for the mirror by increasing its effective thickness.